Cluster tools have been widely used to process objects such as semiconductor wafers for fabricating microelectronic components. Generally, a cluster tool is a robotic processing system that includes loading and unloading modules and a number of different processing modules (PM) placed around a central automated handling unit with one or more robotic arms. It operates by using the robotic arm to transfer the object to be processed from the loading/unloading loadlocks to different processing modules in sequence so as to perform different mechanical or chemical processing, and then back to the loading/unloading loadlocks. The time for the object to stay in the processing module depends on the time needed for a specific processing procedure.
Multi-cluster tools formed by interconnecting cluster tools have also been used for processing and manufacturing objects. Comparing with a single cluster tool, a multi-cluster tool may provide more PMs for manufacturing products of high degree of complexity. In some cases, these tools may also simultaneously process more than one product to provide improved processing efficiency.
Although multi-cluster tools appear to offer some advantages over single-cluster tools, they may include combinations of different types of single-cluster tools (e.g., both single-arm cluster tools and dual-arm cluster tools) which are of different constructions and different scheduling mechanisms. As a result, it would be difficult to determine an optimal scheduling of these tools for maximum operation efficiency.